Cutting insert and tool holder therefor



March 7, 1967 LUNDGREN Re. 26,168

CUTTING INSERT AND TOOL HOLDER THEREFOR Original Filed March 21, 1963 4Sheets-Sheet 1 ATTORNEYS March 7, 1967 E. G. LUNDGREN CUTTING INSERT ANDTOOL HOLDER THEREFOR 4 Sheets-Sheet 2 Original Filed March 21, 1963 W WWATTORNEYS 957 E u. LUNUQREN CUTTING LNSERT AND TOOL HOLDER TI Ni w March21, 1963 INVENTOR ATTORNEYS March 7, 1967 LUNDGREN Re. 26,168

CUTTING INSERT AND TOOL HOLDER THEREFOR Original Filed March 21, 1963 4Sheets-Sheet 4 Fig.15 's- INVENTOR ATTORNEVS United States Patent 26,168CUTTING INSERT AND TOOL HOLDER THEREFOR Evert Gustav Lundgren,Sandviken, Sweden, assignor to Sandvikens Jernverks Aktiebolag,Sandviken, Sweden, a corporation of Sweden Original No. 3,156,032, datedNov. 10, 1964, Ser. No. 266,994, Mar. 21, 1963. Application for reissueOct. 25, 1965, Ser. No. 544,637

11 Claims. (Cl. 29-96) Matter enclosed in heavy brackets appears in theoriginal patent but forms no part of this reissue specification; matterprinted in italics indicates the additions made by reissue.

The present invention relates to a cutting insert for a tool holderhaving a support surface for the underside of the insert and sidesupport surfaces for two supportable side surfaces of the insert, saidinsert having a cutting corner between two adjacent side surfaces andtwo clamp contact surfaces arranged in spaced relation to each other onthe top surface.

Tool holders and inserts of this kind should be built in such a way thatin use the cutting force urges the cutting insert into the insert sitetowards the side support surfaces, which means that the only function ofthe clamping device is to hold the insert when the cutting forces arenot acting upon it. For certain types of work, especially copy turning,it happens, however, that the direction of the cutting force varies somuchin certain cases up to as much as 200-that it is impossible tocomply with the desiderate that the force always urges the insertinwardly against the side supporting surfaces of the holder. This meansthat the insert in certain positions may be pulled or turned from itscorrect position if the clamping device is unable to hold it securely.Practical experience has shown that the friction between the insert andthe support surface alone is often insufficient to hold the insertsecurely.

One of the objects of the invention is to provide a construction inwhich sufficient resistance forces are created to hold the insertagainst movement.

According to the present invention there is provided an arrangement forsecuring a cutting insert in a tool holder with a clamping device whichconsists in providing a surface of the insert with at least one inclinedsurface, the direction of inclination being such that the clamping forceon said contact surface has a component opposed to the cutting force.The inclined contact surface may be provided on the upper surface of theinsert in which case the arrangement restrains the clamping deviceagainst movement in the holder.

The invention further provides a cutting insert for a tool holderequipped with a clamping device said insert having on at least one faceat least one inclined contact surface against which clamping pressure isadapted to be applied, the direction of inclination being such that theclamping force applied thereto has a component opposed to the cuttingforce to which the insert is to be subjected. Where the insert isadapted to be turned over said insert is provided with at least oneinclined contact surface on each of two opposed faces.

The invention still further provides a tool holder for an insertaccording to the present invention wherein said tool holder is providedwith means for restraining movement of the clamping device in saidholder, the locking of the clamping device being essential where saidclamping device bears on said inclined surface; otherwise the clampingdevice and the insert could both be moved together in the tool holder.

According to a preferred embodiment of the invention the insert ischaracterized in that one said clamp contact surface is near the end ofone said adjacent side remote from the cutting corner where saidadjacent side meets a supportable side surface on said insert and saidcontact surface is sloped down in the direction away from the other ofthe said supportable side surfaces.

The invention will now be described more fully with reference to theaccompanying drawings wherein:

FIGS. 1 and 2 are sketches showing different types of work being doneand the force components tending to displace the cutting insert from itscorrect position in the holder,

FIGS. 3 to 6 show a tool holder made according to the invention, FIG. 3being a plan view, FIGS. 4 and 5 being sections along the lines 44 and5-5 in FIG. 3, and FIG. 6 being a fragmentary plan view.

FIGS. 7-9 show an insert for use with such tool holders, FIG. 7 being aplan view and FIGS. 8 and 9 being sec tions along the lines 8-8 and 9-9in FIG. 7,

FIG. 10 is a plan view of an alternative form of insert.

FIG. 11 is a sketch showing the distribution of the clamping forces.

FIGS. 12 and 13 show a tool holder with a modified insert in accordancewith the invention clamped in the holder, FIG. 13 being a frontelevational view and FIG. 12 showing a section along line 1212 in FIG.13.

FIGS. 1416 are enlarged detail views of the insert seen in FIGS. 12 and13, FIG. 14 being a plan view and FIGS. 15 and 16 being sections alongthe lines 15l5 and 16-16 respectively in FIG. 14.

FIGS. 17 to 19 show the shim plate, seen in FIGS. 12 and 13, FIGS. 17and 18 being top plan views and FIG. 19 being a section along the line1919 in FIG. 18.

In FIG. 1 the cutter is shown carrying out a number of differentoperations in the copy turning of a work piece 32. The cutter in eachcase is moving in the reverse direction to the arrows 33, 34 and 35respectively which therefore represent the component of the cuttingforce acting on a parallelogram type insert 31 clamped in a tool holder30. FIG. 2 shows the cutting force components acting on the insert andthe way in which the insert would be displaced in the insert sitecorresponding to the typical examples shown in FIG. 1. In a facingoperation (FIGS. la and 2a) the cutting force component 35 tends to pullthe insert along one side support surface out from the insert site. Thecorrect position of the insert is indicated by the dotted line 36. Inlongitudinal turning (FIGS. 1b and 2b) the cutting force 34 tends toturn the insert around the corner 37. When turning tapering bodies withde creasing diameter (FIGS. 1c and 2c) the cutting force 33 may achievesuch a direction that it tends to turn the insert 31 around the othercorner 38 of the insert site.

FIGS. 3-6 show a tool holder intended for counteracting the abovementioned cutting force components as they tend to turn or pull theinsert from its correct position. The tool holder 30 carries at one ofits ends an insert 31 held fast by a clamping plate 40 and pressedagainst a shim plate 41 by a clamping screw 42. The insert 31 ispositioned with two edge surfaces in contact with edge supportingsurfaces 43 and 44 in the holder. Between the edge supporting surfacesat their intersection a bore 45 is made forming an undercut in order togive ample space for the corner of the insert 31. The clamping plate 40is supported at its rear end by a pointed bearing 46 consisting of apointed lug and a pointed recess. In this way the clamping plate islocked against movement perpendicularly to the axis of the pointedbearing. Closer to the insert site the clamping plate 40 is providedwith a lug 47 which rests against a contact surface 47a on the holdershaft. This contact is maintained because the lug 47 is provided with aninclined surface which cooperates with an inclined surface on an axiallymovable pin 48 situated in the shaft of the holder 30. The pin is urgedupwardly by a spring and urges thereby the lug 47 into contact with thecontact surface 47a. The pin 48 is provided at its lower part with a lug49 which protrudes under the plate 41 and prevents the pin 48 from beingpressed out from its recess in the shaft of the holder when the clampingplate is raised.

The clamping plate 40 engages the insert 31 with two contact surfaces 50and 51. The contact surface 50 on the lug 40a of the clamping plate 40presses against an inclined contact surface 52 formed on the insert,which inclined contact surface is shaped with particular regard to theclamping of the insert 31. The contact surface 51 on the clamping plate40 presses against the upper surface 53 of the insert 31. As can be seenfrom the broken lines representing the surfaces 50 and 51 in FIG. 3these surfaces have a comparatively small area, because a threepointsupport is desired for the clamping plate 40, the three points being thepointed bearing 46 and the surfaces 50 and 51 respectively. In order tofacilitate the selfadjustment of the clamping plate 40 to thisthree-point support the head of the clamping screw 42 rests against tworaised minor projections 54 on the clamping plate 40 which are situatedin line with the pointed bearing 46. In this way a twopoint contact isachieved between the screw 42 and the plate 40 so that the latter canrock around the supporting projections 54, and the screw head does notrestrain the necessary movement of the plate 40 for achieving the stablethree-point support.

FIGS. 79 show in greater detail the insert 31 which at its upper surfaceis shaped as a chip breaker, said upper surface comprising portions 53downwardly inclined from the side cutting edges 55 and curved upwardlycloser to the central part forming upwardly inclined portions 56terminating at a central portion 57, which in the embodiment shown isplane and situated at approximately the same level as the side cuttingedges. 57 can alternatively have a rounded shape and be situated atanother level than the side cutting edges. The side cutting edges 55 areconnected by rounded portions 58 to the end cutting edges 59 situated atthe short sides of the insert 31. As the insert 31 is symmetrical it canbe turned through 180 around an axis perpendicular to its under surface60. The insert 31 may also be formed without the central portion 57 andhave inclined surfaces 53 only towards the middle.

The earlier mentioned surfaces 52 are intended to be support surfacesfor the contact surface 50 of the clamping plate 40. As appears fromFIG. 3 only the surface 52 which is situated adjacent the outer sidecutting edge has contact with the clamping plate. The other surface 52has no contact with the clamping plate 40, the contact surface 51resting on an upper surface 53 of the insert. The upper surfaces 53 maybe parallel with or inclined in relation to the under support surface 60of the insert.

As appears from FIG. 9 the surfaces 52 may be inclined from the middleand downwardly towards the long sides of the insert but horizontal inthe longitudinal direction of the insert (52 in FIG. 8). They may,however, also be inclined in the longitudinal direction from the shortsides downwardly as is indicated by broken lines in FIGS. 7 and 8. inwhich case they assume another position marked 52a.

In use, by aid of the inclination of the surfaces 52 and the uppersurfaces 53 of the insert, the clamping plate 40 will maintain an edgesurface 55 of the insert 31 in contact with the edge supporting surface44. If the surfaces 52 are also inclined to the position 52a the insertwill be also maintained in contact with the other edge support surface43. Even if the inclinations of the contact sur faces are smaller thanthe so-called self-locking angle, which means that the insert is notactively urged in the direction towards the edge supporting surfaces,the passive resistance against displacement from the edge supportingsurfaces will nevertheless be very great. The inclination of theinclined surfaces 52 or 520 in the section shown in FIG. 9 should liewithin the range l0-60 The central portion I in relation to the undersurface 60 and preferably 20 30". The inclination in the section shownin FIG. 8 should be 045, preferably 1040".

As the clamping plate is supported against sideward movement by thepointed bearing 46 and the abutting support 47 an effective and firmlocking of the insert 31 in all directions without play will beachieved. The friction between the insert and the shim plate 41 andbetween the insert and the clamping plate contributes of course to thelocking.

As appears from FIGS. 79 the inclined contact surfaces 52, 52a arecomparatively small in relation to the rest of the insert 31, and it isof course desirable that they occupy as little space as possible alongthe sides which carry the cutting edges.

For the insert plate shown which has the shape of a parallelogram theangle of the cutting corners can be between 45 and 88". It is of coursealso possible to give the insert a rhombic shape. Cutters of rectangularplan shape may be used, i.e. the corner angles being 90. With suitablemodification of the holder alternatively the insert may have more thanfour corners, in which case the cutting corner angle becomes obtuse.Inserts formed as a parallelogram have been found especially suitablefor copy turning-21 type of work where the present invention as earliermentioned is especially useful.

In FIG. 10 an alternative embodiment of insert is shown where theportion 57 is oblique in relation to the cutting edges 55 in order toprovide sufficient room for the contact surface 51 of the clamping platefor inserts Where the chip breaker surfaces 53 and 56 have little width.

FIG. 11 shows how the resultant force R of the clamping forces issituated comparatively centrally in spite of the fact that the latterare obliquely directed. The horizontal component H is received by theside support surface. By placing the clamping forces symmetrically onboth sides of the insert the resultant force R is brought closer to themiddle of the supporting surface than for a one-sided position of theforces acting on the insert.

FIGS. 12 and 13 show an alternative embodiment of the insert and theclamping plate where the top of the insert is not shaped as in theearlier example with a chip breaker on its surface.

FIGS. l4l6 show an insert according to this last mentioned on a largerscale.

The holder shaft 71 (FIG. 12) is unchanged in comparison with the shaft30. The clamping plate differs from the clamping plate 40 in the shapeof one of the small surfaces 73 and 74 which contact with the insert 72.As the top surface 75 of the insert is parallel with the under surface77 the surface 73 must also be parallel with the under surface asdistinguished from the surface 51 shown in FIGS. 3 and 5. The surface 74shall as earlier shown have the same inclination as the inclined contactsurface 76 against which it abuts. On analogy with the earlier describedembodiment the inclined contact surfaces 76 can be either parallel withthe surface of the insert in the longitudinal direction or inclinedthereto as indicated by broken lines in FIGS. 14 and 15 showin analternative position 76a for the inclined contact surfaces. In thesection shown in FIG. 16 the surface 76 or 76a is always inclined. Forthe inclination angles the above statements about the surfaces 52 and52a respectively are valid. This embodiment has been illustrated for aninsert which in plan has the shape of a parallelogram, and the angle ofthe cutting corners may be 45-88.

In order to still more effectively prevent turning of the insert inrelation to the shim plate and also achieve full certainty that theinsert is well supported at the edges, the shim plate can be made with araised ridge along the edge of the upper surface or several raisedportions situated at the edge. A shim plate 41 (FIG. 17) is providedalong its edge with a ridge 61. In the centre of the plate there is ahole 63 for a screw, a tubular pin or similar device for holding theplate on the tool holder. Between the screw hole 63 and the ridge 61 isa portion 62 which is somewhat lower than the ridge 61, which portion,as shown, suitably can be in the main plane. The ridge 61 is ground to aplane shape in the same way as the insert, by which means a good contactis achieved along the edges of the insert. If the shim plate hand anunbroken plane top surface the contact between the underside of theinsert and the top side of the shim plate might be concentrated to thecentre of the contact surface because of tolerances in the finish of thesurfaces causing a minor convexity, the result of which would be thatthe contact at the edge would be bad and the risk would arise of theinsert being broken by the cutting forces. Moreover, a contact in thecentre gives very small resistance against turning of the insert, sothat the friction between the insert and the shim plate caused by theclamping force would in such case have a very small effect forpreventing the turning of the insert. When the contact occurs along theperipheral ridge 61 the friction force has a long lever-arm, and theresistance against turning is as effective as it is possible to make it.In FIGS. 18 and 19 is shown an alternative embodiment of the shim platewhere the ridge 61 is substituted by two raised portions 64. It is alsopossible to limit the raised portions to the areas closest to thecorners of the insert, thereby achieving a support with four separateraised portions. A special advantage from one or more raised portions 61or 64 is that only the said portions have to be accurately surfacefinished, while neither of the lower portions 62 between the screw hole63 and the raised portion 61, and between the raised portions 64 requirean accurate finish. It is of course also possible to provide the underside of the insert with raised portions at the periphery, said raisedportions facing the shim plate, the shim plate being either plane orhaving corresponding raised portions.

If the shim plate is composed of several plates placed on top of eachother, these may in order to prevent mutual turning and rocking havecontact with each other and at the bottom also with the tool holder bysimilar raised peripherical portions on the plates and possibly also onthe tool holder.

The invention has been described and illustrated above in connectionwith turnable inserts, i.e. inserts that can be turned around, and itcan of course also be used for inserts which can be turned over end forend, in which case both sides of the inserts are provided with inclinedcontact surfaces in accordance with the invention. The invention canalso be used for such inserts which are not turnable and have only onecutting corner. The described inserts are four-sided, but the inventioncan be applied also to triangular inserts or inserts having more thanfour sides.

The insert is usually made of sintered materials such as sinteredcarbide or ceramic oxides. Also the shim plate can be of such materials.The other parts of the tool holder are usually made of steel.

As appears from the examples above described the invention provides asubstantial advantage in that inserts in the tool holder can beeffectively held against displacement from their correct position insuch working operations where such risk is involved in connection withhitherto known devices. This is of great importance for work of highaccuracy as for instance in copy turning.

I claim:

1. A cutting insert having a bottom surface, a top surface, sidesurfaces between said bottom and top surfaces and corners at thejunctures of adjacent side surfaces, a cutting edge along theintersection of at least one of said side surfaces and said top surface,one only of the two corners between which said one side surface extendsbeing a cutting corner, a clamp contact surface constituting only aminor part of said top surface adjacent to the other of said twocorners, said clamp contact surface being outwardly and downwardlyinclined in relation to said bottom surface, and approaching said bottomsurface in the direction toward said one side surface, said outwardlyand downwardly inclined clamp contact surface having a length in thedirection of said one side surface Which is only a minor part of thelength thereof, and another part of said top surface spaced from saidoutwardly and downwardly inclined clamp contact surface providing asecond clamp contact surface.

2. A cutting insert as defined in claim 1 in which said outwardly anddownwardly clamp contact surface approaches said bottom surface also inthe direction towards said cutting corner.

3. A cutting insert as defined in claim 1 in which said outwardly anddownwardly inclined clamp contact surface is a plane surface.

4. A cutting insert as defined in claim 1 in which a. part of said topsurface adjacent to said outwardly and downwardly inclined contactsurface is formed as a chip breaker and is inclined inwardly away fromsaid cutting edge and downwardly toward said bottom surface in thereverse direction to said outwardly and downwardly inclined clampcontact surface.

5. A cutting insert as defined in claim 1 comprising a second cuttingedge along the intersection of said top surface and the other of the twoside surfaces meeting at said one cutting corner.

6. A cutting insert as defined in claim 1 comprising at least twonon-adjacent cutting edges along the intersections between said topsurface and at least two non-adjacent side surfaces, each of saidcutting edges terminating at one of its ends at a cutting corner and atthe other of its ends at an outwardly and downwardly inclined clampcontact surface.

7. A cutting insert having a substantially plane rhonibodial bottomsurface, substantially plane side surfaces extending substantiallyperpendicularly from said bottom surface, a top surface joining saidside surfaces, a cutting edge at the intersection of each long sidesurface with said top surface, a cutting corner at each acute anglecorner, an outwardly and downwardly inclined clamp contact surfaceconstituting only a minor part of said top surface adjacent to eachobtuse angle corner, each outwardly and downwardly inclined clampcontact surface being inclined downwardly adjacent to one end of onecutting edge toward said bottom surface in the direction toward theadjacent long side surface, and a portion of said top surface adjacentto [the other end of each cutting edge] each outwardly and downwardlyinclined clamp contact surface constituting a second clamp contactsurface.

8. A cutting insert as defined in claim 7 in which said top surfacebesides said outwardly and downwardly inclined clamp contact surfacesadjacent the obtuse angle corners, comprises an inwardly and downwardlyinclined surface extending away from each cutting edge toward the longaxis of the insert and downwardly toward said bottom surface and asubstantially plane surface parallel to said bottom surface and betweenthe last named inclined surfaces.

9. A tool holder for a cutting insert comprising a holder shaft havingan insert site therein, said insert site having a bottom surface and twoside surfaces adapted to be engaged by the bottom and two side surfacesof an insert positioned therein, a clamping plate for clamping an insertin said insert site, a screw extending through said clamping plate intosaid holder shaft for pressing said plate against an insert in saidinsert site, said plate having two spaced apart insert contact surfaceson downwardly projecting portions thereof positioned over said insertsite and adapted to engage an insert and means in addition to said screwfor preventing laterial movement of said plate with respect to saidinsert site, said insert contact surfaces being placed adjacent the freeend portions of said side surfaces.

10. A tool holder as defined in claim 9 in which one of said insertcontact surfaces is positioned on a sidewardly projecting portion onsaid clamping plate extending along one of said side surfaces.

11. A tool holder and cutting insert combination comprising an inserthaving a substantially plane bottom surface, substantially plane sidesurfaces and a top surface, a cutting edge at the intersection of one ofsaid side surfaces and said top surface, said top surface comprising aclamp contact surface adjacent to one end of said cutting edge andextending downwardly toward both said bottom surface and said one sidesurface and a second clamp contact surface spaced from said one clampcontact surface, said holder comprising a shaft having an insert site,said insert site having a bottom surface and side surfaces engaging thebottom surface and two adjacent side surfaces of said insert, a clampingplate, a screw holding said clamping plate against said insert and meansother than said screw holding said clamping plate against laterialmovement with respect to said insert site, said clamping plate havingtwo spaced apart clamping areas engaging said clamp contact surfaces onsaid insert, said clamp contact surfaces being positioned adjacent thefree ends of said side surfaces in said insert site.

References Cited by the Examiner The following references, cited by theExaminer, are of record in the patented file of this patent or theoriginal patent.

WILLIAM W. DYER, 111., Primary Examiner.

HARRISON L. HINSON, Examiner.

